Field of the Invention
The present invention relates to a skinned panel whose core material is covered with a skin material sheet and a molding technology thereof.
Related Art
The skinned panels have been conventionally used for various objects or purposes including the transportation machines (e.g., automobiles and airplanes), the building materials, the housings of the electrical equipment, and sports and leisure activities. The skinned panels basically have a structure in which a core material is covered with single or plural skin material sheets, and are classified into the following types. One has a structure that only one side of the core material is covered with a skin material sheet. The other has a structure that both sides of the core material are covered with skin material sheets. For example, the skinned panels, having the structure that one side of the core material is covered with the skin material sheet, are used for objects such as the building materials. In the objects, that the other side of the core material is not required to be covered with the skin material sheet because the other side of the core material is not visible for a user. On the other hand, the skinned panels, having the structure that the both sides of the core material are covered with the skin material sheets, are also referred to as the sandwich panels. The sandwich panels are composed of two skin material sheets and a core material interposed therebetween. In other words, the sandwich panels are basically formed by a laminated structure of a skin material sheet, a core material, and a skin material sheet.
PCT Patent Application Publication No. WO2009/136489 discloses a method of molding a sandwich panel using a pair of split molds and a pair of molten resin sheets made of a thermoplastic resin material. In the molding method, molding of skin material sheets and welding of the skin material sheets and a core material are simultaneously achieved under a condition that the core material is interposed between a pair of the molten resin sheets extruded out of T-dies within the pair of split molds. Further, the publication discloses a method of molding a preferable core material and a method of molding a sandwich panel when a sandwich panel made of a resin is applied to a cargo floor lid of an automobile, for instance. In other words, the publication discloses a method of molding a sandwich panel and a method of molding a core material having a complex outline for accommodating the sandwich panel in a limited space within an automobile.
Now, specifications required for the skinned panels depend on purposes. For example, it is required for the skinned panels to achieve both reduction in weight and enhancement in stiffness when a sandwich panel made of a resin is used for the cargo floor lids of the automobiles as a skinned panel. The cargo floor lids are generally used for putting heavy loads thereon. Therefore, the cargo floor lids are required to have a stiffness (especially, a flexural stiffness) enough to endure the weight of the loads. Simultaneously, the cargo floor lids are required to have a light weight in terms of enhancement in fuel economy of the vehicles. According to the publication, reduction in weight and enhancement in stiffness, which are the required points, are both achieved by a relatively light core material with a hollowed part and skin material sheets having a stiffness greater than that of the core material.
The skinned panels have been recently requested to simultaneously ensure a high stiffness and achieve further reduction in weight for the cargo floor lids of the automobiles but also for other objects such as the bathtub covers. In response to the request, the inventor of the present application tried to form a skin material sheet thinner than the conventional one in order to achieve reduction in weight of a skinned panel. However, this turned out to be difficult because of the following reasons. First, a thin resin sheet cannot be sufficiently welded with the core material, because it is rapidly cooled down and solidified immediately after it is extruded. Second, the extruded resin sheet has a high chance of producing a so-called curtain phenomenon that the surface of the resin sheet is formed in a wavy shape, because it is thinly formed. When the curtain phenomenon is produced in the resin sheet, some portions of the resin sheet are welded before molding. A molding performance is thereby deteriorated within the split molds.
In view of the above, an aspect of the present invention addresses a need to provide a skinned panel for stably forming a thin skin material sheet and a molding method thereof.